Story related. After defeating the Snake Triad boss you have an interesting section. Those who played 0 already know what is going on the instant the see Kiryu on a highway. Once again we have an on-rails shooter section. The final guy is the driver of the 18-wheeler. Take him down and the section ends along with the chapter giving you the Achievement. (This is your reminder for each game that Kazuma Kiryu has never killed a man according to the series)